In coolants (antifreeze) formulations for internal combustion engines, including glycol-type coolants, alkali metal silicates are often added for corrosion inhibition. Silicates are believed to inhibit corrosion by forming a thin protective layer over metal surfaces of the coolant system. Such alkali metal silicates (generally the commercially feasible sodium or potassium silicates) are the best known protection against corrosion of aluminum cooling system and engine components.
The use of aluminum parts in the automotive field has increased in recent years. Aluminum radiators are found in many newer-model passenger cars. Many imported medium-duty engines contain several aluminum parts. Some aluminum cooling system components have been incorporated into some new heavy-duty engines. The use of aluminum parts is expected to further increase in the future because of aluminum's machinery and weight savings costs.
Responsive to such increasing use of aluminum, manufacturers of coolants for internal combustion engines have generally increased the silicate content therein. Silicate levels in many commercial coolants have increased about three- to eight-fold in the past several years. A typical undiluted coolant contains about 1400 ppm silicate as SiO.sub.2. For most parts of the United States the recommended dilution of coolant concentrate is 50:50 with water, but this drops to about 60:40 coolant to water in areas that experience severe cold conditions, such as in the North and Northwest areas of North America. Coolant additives or conditioners may themselves contain silicate and thus increase the overall silicate level of the coolant during use.
The level of silicate in a given cooling system may be higher than comtemplated by coolant and additive manufacturers, for instance if a mechanic tops-off the coolant in the system with straight concentrate instead of diluting it with water, or when additives or conditioners are added in amounts greater than recommended dosages.
There have been an increasing number of instances of deposits dropping out of coolants, which problem is believed in part attributable to the high silicate levels in the coolant, possibly aggravated by high engine temperatures used for increased fuel burning efficiency, the presence of phosphate corrosion inhibitors and calcium and magnesium ions of hard water, the heat-cool cycles of diesel engines, and low-flow cooling systems with smaller-diameter radiator tubes. Such deposition problems, discussed in more detail below, can reduce the efficiency of the cooling system leading to engine overheating, and can cause damage to the water pump and other progressive engine damage. Once formed such deposits, gels often containing abrasive particles, are extremely difficult to eliminate from the cooling system.
While glycol-based low-silicate coolants are still to be found commercially, they are not widely available because unsuitable for many engines, they are often more expensive, and their use may not be wholly preventive of coolant deposits. Deposit drop-out can also be a problem under some conditions with coolants containing no silicates, for instance coolants containing high levels of phosphates.
It is thus highly desirable to provide a composition that stabilizes such coolants, preventing the fall out of gelled deposits in the first instance. It is highly desirable to provide such a stabilizer that is effective in the presence of phosphates and calcium and magnesium ions and other aspects of the chemical environment under us conditions. It is desirable that such stabilizer be effective with both low and high silicate coolants and regardless of whether additives or conditioners are incorporated into the coolant at recommended or higher than recommended dosages. It is desirable that such stabilizer be effective while not interfering with the corrosion inhibition system of the coolant.
U.S. Pat. No. 3,288,846 (Irani et al.) describes processes for manufacturing aminoalkylenephosphonic acids and notes that the relatively lower molecular weight ones are useful as water softening agents in boiling water, for example, to prevent iron precipitation. U.S. Pat. No. 3,303,139 (Blaser et al.) discloses aminophosphonic acid metal ion complex formers particularly for polyvalent metal ions and methods for preparing such compounds. U.S. Pat. No. 3,483,925 (Slyker) discloses a method of treating oil wells to inhibit the deposition of scale comprising the use of a viscous polymer solution and a solution of scale inhibitor; the scale inhibitor is preferably an organic phosphonate. U.S. Pat. No. 3,630,938 (Troscinski) discloses scale formation inhibition and corrosion prevention in water or brine with the combination of certain chromate compounds and organic phosphonate compounds. U.S. Pat. No. 3,723,333 (Freyhold) discloses substituted alkylene diphosphonic acids/salts together with water-soluble, complex-forming compounds containing at least one phosphonate or N-dimethylenephosphonic acid group for the prevention of corrosion and mineral depositions. U.S. Pat. No. 3,886,204 (Geffers et al.) discloses phosphonoalkyldicarboxylic acids having complex-forming effect on alkaline earth metal ions. U.S. Pat. No. 3,960,576 (Carter et al.) discloses the use of inorganic silicate-based compositions together with an organic phosphonate and carboxy methyl cellulose for corrosion inhibition. U.S. Pat. No. 4,026,815 (Kallfass et al.) discloses inhibition of corrosion and scale formation with phosphonocarboxylic acids.
U.S. Pat. No. 4,287,077 (Wing) discloses the addition of a glycol soluble ether-modified silicone to aqueous glycol and glycol ether compositions containing silicates and other corrosion inhibitors to prevent silicate gelling during storage. U.S. Pat. No. 4,333,843 (Wing et al.) discloses organophosphorussilicon hydrolyzates for preventing gelation during storage of aqueous glycol and glycol ether compositions. U.S. Pat. No. 4,367,154 (Jernigan) discloses the use of organo-silicon phosphonates for rendering glycol concentrates containing alkali metal silicates gelation resistant; such compounds contain trialkoxy - silyl, alkyldialkoxy - silyl, or dialkylalkoxy - silyl groups. U.S. Pat. No. 4,457,852 (Bosen) discloses organomercaptosilanes having a reactive group causing the mercaptosilane to form a silanol when hydrolyzed for improving the anti-gel characteristics of silicate-containing antifreeze compositions. U.S. Pat. No. 4,462,921 (Peterson et al.) and U.S. Pat, No. 4,466,896 disclose organosiloxane stabilizers for silicate-containing antifreeze/coolant compositions.